Isolated board-mounted power (BMP) modules typically have an input on the primary side which is designed to enable or disable the module output (an “ON/OFF” input) based on a signal issued by the using system. If the controller of the power module is on the primary side (input side), the interface to either a dedicated hardware circuit like a comparator, or the input to a processor which controls the output of the power module is usually simple and straightforward.
Power module designs incorporating a processor or controller, such as a microprocessor on the secondary side present the challenge of bringing the primary side information, such as input ON/OFF, input undervoltage/overvoltage shutdown, startup input faults, switching frequency, etc., across the isolation barrier. An isolation barrier is employed to provide galvanic isolation which prevents the flow of dc currents between functional sections of an electrical system. For an isolated power module the isolated functional sections may be the primary or input section and the secondary or output section. In most cases, primary side information is transferred across an isolation barrier by dedicated single-purpose devices such as opto-couplers or magnetic means using a signal transformer.